3.2. Eco-sphere total emissions
Fig. 3 shows the GWP for all simulated locations/cropping systems
and tillage management. Sequestered carbon provided the
main offset to total emissions and increased with tillage reduction.
The amount of sequestered carbon decreased with lower precipitation
due to the effects of declining cropping intensity (the proportion
of fallow years increases as precipitation falls) and lower
yields producing less residue inputs. The allocated N2O emissions
and emissions from fertilizer production decreased in the lower
rainfall areas as less N fertilizers were used. Fuel consumption decreased
with decreasing rainfall, biomass production and tillage,
thus directly impacting emissions from fuel. In the low rainfall
zone (Lind), there was little difference in fuel consumption between
CT and RT, as mechanical weed control is replaced with
chemical weed control. Emissions from other auxiliary processes
such as equipment and pesticides productions (not shown) were
less than 2% of total emissions.
3.3. Value-sphere carbon credit
Fig. 4 shows the value-sphere carbon credit of converting from
CT to RT or NT, and the savings/extra cost of reducing tillage. All NT
and RT achieved value-sphere carbon credit (based on $2.48/Mg
CO2e) of about 0.27–1.63 $ ha1 year1
. In the high and moderate
rainfall zones, the value-sphere carbon credit represents additional
profit, as the RT and NT systems are more profitable than the CT
systems. At 0.46 $ ha1 year1
, the value-sphere carbon credit for
RT in the low rainfall areas is well below the breakeven as profit
Fi